Quantitative parameters in an environment such as temperature, humidity, pH, viscosity, velocity, density, distance, acceleration, liquid and gas flow, chemical composition, gas analysis, electrolyte analysis, vibration frequency, strain, pressure, radiation, and particle counts are a few of the critical gauges in characterizing any environment. These parameters influence dynamic and static mechanical, physical, electrical, chemical, and diffusive properties of the environment.
Occasionally, these parameters must be monitored or calibrated to authenticate the stability or state of the environment. In particular, this disclosure addresses the environment used for various industries such as farming, mining, construction, non-electrical machinery, transportation equipment (including automobiles), food products, chemicals (including petrochemicals), electrical and electronic equipment, textiles, utilities, and the natural environment in which we live.
Applications to Process Control and Monitoring with Factory Automation
Industrial technology has increasingly become capital intensive, and has displaced both skilled and unskilled workers. The term automation, coined from the words automatic and operation, describes all such processes in which mechanical and/or electronic devices are employed to carry out tasks without human intervention.
Currently, and into the future, manufacturing assembly lines will involve less human intervention through the use of factory automation and robotics. One example of an industry that has incorporated a high level of factory automation is integrated circuits (IC), flat panel displays, microelectromechanical devices (MEMs) and other electrical materials. Other industries with an increasing focus on automation include farming, mining, construction, non-electrical machinery, transportation equipment (including automobiles), food products, chemicals, electrical and electronic equipment, and clothing.
The demands on manufacturing continue to increase, in order to foster continuous improvements in efficiency, throughput, cost reduction, performance, and stability. This allows companies to maintain profitability in a highly competitive market.
Manufacturing process stability requires stable equipment. The objective is for every tool to perform like every other such tool, with no unique signatures. An appropriate combination of well engineered tools and appropriate metrology is necessary to maximize productivity while maintaining acceptable cost of ownership.
To minimize this variation, state-of-the-art manufacturing equipment come installed with permanently attached electronic sensors. These sensors are positioned in close proximity to the area of interest, and linked to computers that monitor any variation in the data, and are trigged by alarms if established tolerances are exceeded.
Similar to other quantitative measuring devices, this data is not accurate unless the sensor is calibrated to a known standard. Otherwise, the measurement can not be universally compared with other sensors measuring the same parameter. To calibrate the permanently installed sensors, another temporary sensor, that measures the same parameter, is routinely used. This temporary sensor may either be previously calibrated to National Institute of Standards and Technology (N.I.S.T.) to provide absolute measurement values, or it is an “internal” standard, to baseline the parameter against other systems in the same manufacturing facility, corporation, or institution.
Measurement Parameters of Interest
Quantitative parameters in an environment such as temperature, humidity, pH, viscosity, velocity, density, distance, acceleration, liquid, plasma, and solids analysis, vibration frequency, stress/strain, pressure, radiation, and particle counts are a few of the critical gauges in characterizing any environment.
Temperature
One of the most important and commonly measured parameters is temperature. The word “capital goods” will be used in this context to address the manufactured solid, liquid, or gas of interest. Capital goods temperature, is a very influential parameter in controlling the physical properties, and reaction kinetics during process manufacturing. As such, control of temperature and uniformity of temperature, is a key parameter for achieving process control. Common techniques include sensors such as thermocouples, platinum resistors and silicon diodes, which are immersed in the environment of the capital goods.
Other methods of temperature measurement included radiation thermometry or pyrometry. Radiation pyrometry involves measuring long wavelength radiation from an object and making a temperature determination on the basis of that measurement. Radiation pyrometry has several disadvantages. Among these disadvantages is the reliance on a surface optical emissive properties which vary with temperature, and surface/subsurface physical properties. Another non-contact method for measuring surface temperature is with a fluroptic sensor. This technique uses a laser probe, which records the temperature dependent decay rate of a phosphor coating on the capital goods surface.
Flow rate
Common methods for measuring flow rate include “paddle wheel” and hinged vane type transducers. For lower flow rate and when size and weight limitations are considered, higher accuracy can be obtained using thermally based anemometers and liquid flow meters. This technique measures the differential temperature between two sensors, or alternatively, measures the energy required to maintain a heated resistance wire at constant temperature.
Distance
Common methods for measuring distance include ultrasonics, radar, and linear variable differential transformers.
Particles
Many of our modern, high technology industrial practices demand cleanliness. Specifically, they demand an absence of particle contamination. For example, microelectronic and micromechanical devices demand cleanliness since particles as small as 50 nm may cause a degradation in the product yield. Another example may be drawn from the pharmaceutical industry: A parenteral (injectible) drug must be free of particles that could block a blood vessel, causing a stroke (interruption of blood supply to part of the brain) or necrosis (interruption of blood supply to a tissue). The drug maker, as well as the microelectronic/micromechanical maker, has to manage the production environment to eliminate particle contamination.
The basic methods of particle detection employ HeNe lasers, laser diodes, photodiodes, and support equipment. Particles are introduced through inlet jets when monitoring aerosol or gas media, or through capillaries when monitoring liquid media. Laser power illuminates the particles in the sample cavity. The particles produce a pulse of light that is detected by a photodiode. The photodiode converts the pulse to an electrical signal (converts current to voltage), amplifies the voltage, and compares the pulse voltage to a set of thresholds. If a particle exceeds one threshold but not the next greater threshold, the instrument places the particle into the lower threshold. The threshold value corresponds to the size of the particles, and the frequency of scattering events corresponds to the quantity of particles in the sample volume.
Humidity
Relative humidity is a difficult physical parameter to transduce, and most transducers available require complex signal conditioning circuitry. Common methods include measuring the change in resistance or capacitance of a sensor in contact with the environment.
Pressure
Common methods for measuring pressure include: a) barometers (capacitive, bonded strain gauge and semiconductor transducers), b) manometers (difference in height h of two mercury columns, one open to the atmosphere and the other connected to a source of known pressure), c) Bourdon tubes (a tube that straightens out when the internal pressure exceeds the external pressure, d) Aneroid (thin flexible ends of an evacuated chamber that are pushed in or out by an external pressure) and d) ion gauges.
Viscosity
The viscosity of a fluid is given a quantitative definition in terms of an experiment in which a plate of area A is pulled across a layer of fluid s thick. For most fluids, it is found that the force F required to pull the plate at a constant speed v, is proportional to A and v, and inversely proportional to s.N=F*s/A*v 
Radiation
Unstable atomic nuclei emit three kinds of radiation:                Alpha particles        Beta particles        Gamma particlesA magnetic field is used to quantify each of these particles. With a magnetic field directed into the page, the positively charged alpha particles are deflected to the left, and the negatively charged beta particles are deflected to the right. Gamma rays carry no charge and are not affected by the magnetic field.        
Other More Advanced Chemical/Material Analysis Techniques
Many techniques exist for characterizing liquids, gases, plasmas and solids. These include, but are not limited to:                electron beam instruments                    1. Energy dispersive x-ray spectroscopy (EDS)            2. Cathodoluminescence (CL)                        x-ray/electron diffraction and scattering        electron/x-ray emission spectroscopy                    1. x-ray photoelectron spectroscopy (XPS)            2. Ultraviolet Photoelectron Spectroscopy (UPS)            3. Auger Electron Spectroscopy (AES)            4. Reflection High Energy Electron Diffraction (REELS)            5. X-ray Fluorescence (XRF)                        visible/UV emission, reflection and absorption                    1. Photoluminescence (PL)            2. Modulation Spectroscopy            3. Variable Angle Spectroscopic Ellipsometry (VASE)                        Vibrational Spectroscopy                    1. Fourier Transform Infrared Spectroscopy (FTIR)            2. Raman Spectroscopy            3. Solid State Nuclear Magnetic Resonance (NMR)                        Ion Scattering                    1. Rutherford Backscattering Spectroscopy (RBS)            2. Elastic Recoil Spectroscopy (ERS)            3. Ion Scattering Spectroscopy (ISS)                        Mass/Optical spectroscopy                    1. Residual Gas Analyzer (RGA)            2. Dynamic/Static Secondary Ion Mass Spectroscopy            3. Laser Ionization Mass Spectroscopy (LIMS)            4. Sputtered Neutral Mass Spectroscopy (SNMS)            5. Glow Discharge Mass Spectroscopy (GDMS)            6. Inductively Coupled Plasma Mass Spectroscopy            7. Inductively Coupled Plasma/Optical Emission Spectroscopy                        Neutron/Nuclear Spectroscopy                    1. Neutron Diffraction            2. Neutron Reflectivity            3. Neutron Activation Analysis (NAA)            4. Nuclear Reaction Analysis (NRA)Details on these measurement techniques can be found in ref. [3, Encyclopedia of Materials Characterization, C. R Brundle, C. A. Evans, S. Wilson, C 1992, Reed Publishing, pp 1–750.]Measurement Accessibility                        
In high volume mass production, capital goods are manufactured rapidly through machines or tools using fully automatic robotic handling. In many instances, the environment within the machine or tool may be inaccessible to place a measurement probe at the point of interest. For example, robotic handling equipment may be used to transfer the capital goods through small openings and air locks, and into a series of vacuum chambers, or into chemical tanks, furnaces, hot plates, plumbing, or light exposure stages. In addition, capital goods are introduced into hostile environments such as extreme temperatures, poisonous gases, low pressure (i.e. vacuum), acid or basic solutions, or radiation.
The aforementioned factors inhibit the ability for fast and non-intrusive capital goods measurement. More specifically, the manufacturing equipment may stop regular production for an extended period of time. In many instances, the system must be purged of all inhospitable environments, then dismantled to allow manual placement of the measurement device into the process area of interest. Next, the system must be returned to the standard process conditions before any measurements can be made. After the measurement is complete, the system must be purged again of all inhospitable environments, and the calibration device is removed. Finally, the system is returned to the standard process conditions before the equipment is returned for normal processing. This extended downtime is costly and laborious.